Method of making insulated wire of small or irregular cross-section



June 16, 1942. w PATNQDE METHOD 0F MAKING INSULATED WIRE OF SMALL 0R IRREGULAR CROSSSECTION Filed Nov. 18, 1940 Fig. 1.

IIVJ'ULAYTHVG coflravw 41966450 Comments 7' or 41v Inventor: Winton I. atnode,

His Attorney.

Patented June 16, 1942 METHOD OF MAKING INSULATED OF SMALL OR IRREGULAR CROSS-SECTION Winton L Patnode, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application November 18, 1940, Serial No. 366,176

1 Claim.

been insulated by extrusion of a hot, plastic resinous insulation thereon, which becomes hard upon cooling. Ordinarily, the magnet wires insulated or coated by'either of these methods are of circular cross-section, and although wires of square or rectangular cross-section have been so insulated, the coating of wires of other than circular cross-section has always been kept to a minimum owing to two disadvantages in the processes. In the first place, coating a rectangular wire with an enamel or similar liquid composition by the conventional method of drawing the wire through a bath of the liquid composition and then baking the coating to harden it, results in a coating that is thick on the fiat surfaces of the conductor and very thin on the edges or angular parts of the conductor. Consequently, in order adequately to insulate the edges or more angular parts of the conductor, it is necessar to apply much more material to the fiat portion than is necessary or desirable. In the second place, the insulation of wires of rectangular cross-section by extrusion of the hot, plastic, resinous composition around the wire, as it is drawn through a rectangular die, is an uneconomic process, owing to the large number of different sizes of dies which are necessary. For example, the electrical industry uses at least a thousand different sizes of rectangular wires. They usually are insulated by wrappings of textiles or paper. The insulation of very fine round wires, for example, less than 0.002 inch in diameter, is a diflicult and expensive process owing to the fact that most liquid coating materials tend to form beads along the wire rather than to spread out in an even continuous coating, and also owing to the fact that the very low tensile strength and almost invisible size such-wires require very special machinery and technique. I

The toregoing disadvantages of coating wires with thin films oi! resinous material have pracwires of greater than 0.002 inch in diameter and wires of less than this diameter or of non-circular cross-section are seldom insulated with a thin film of resinous material, in spite of the fact that there are great advantages to be attained through the use of such wires. For example, thin films of resinous insulation are generally superior to other types of magnet wire insulation, and rectangular wire effectively occupies less space when wound into a coil than does round wire of the same cross-sectional area.

No difiiculty presents itself ordinarily in coating metallic conductors of average size circular cross-section by the conventional, enameling process. It has, however, not been possible to reduce the diameter of the insulated wire once the enamel film is in place because the mechanical operations incident to such processes as rolling, drawing or swaging removed or destroyed the insulation film.

I have discovered that conductors insulated with polyvinyl acetal type materials, that is, resinous compositions comprising the reaction product of an aldehyde with a hydrolyzedpolymerized vinyl ester, lend themselves to such mechanical treatment as above noted and can be reduced in size or shape without injury to the insulation film. Although it has been known that such coated wires can be deformed mechanically as by bending or hammering at any particular point without injury to the insulation at the point of deformation, it was not expected that such insulated wire could be continuously altered in cross-sectional size and shape, as by rolling, drawing or swaging, and despite such drastic ,mechanical treatment of the film, preserve its continuity which is essential in the production of insulated wire. 1

The advantages of this discovery will be readily apparent when it is realized that the process described herein overcomes the difiiculties inherent in the previous methods of manufacturing conductors of comparatively small diameter or conductors of substantially non-circular crosssection provided with uniform resinous insulating coatings. As coating dies and the like are best adapted to the coating of circular wire, the present invention permits the use of the usual coating apparatus for applying the polyvinyl acetal resins to the wire which, after baking to harden the film, can be passed through ordinary rolls, such as turks head rolls, to produce flat or substantially rectangular wire, or drawn through the usual wire drawing dies to produce wire of tically restricted the industry to the use of round small size or cross-section without impairing the continuity of the insulating film. Furthermore, the hereindescribed process permits a Substantial saving in cost, since wires of many difi'erent cross-sectional dimensions can be manufactured from one standard round insulated wire.

In accordance with this invention, a wire 0.032" in diameter coated with a 0.001" layer of the polyvinyl acetal resin enamel can be continuously cold rolled to a flat or substantially rectangular wire approximately 0.015" thick and 0.047 wide without breaking the insulating film. Again, a wire having a diameter of 0.0089" and an insulating coating 0.0008" thick can be rolled by passing the wire through suitable rolls until a flat wire 0.006" by 0.0141" was obtained. This wire, when tested for insulation breakdown by dipping the wire connected to one electric supply lead into a bath of mercury connected to the other supply lead, shows no breaks in the insulating film under ordinary voltage requirements whereas wires insulated with ordinary enamels will show numerous breaks in the enamel after being subjected to the rolling treatment. Since it effectively occupies less space when wound into a coil than round wire of the same cross-sectional area, the flat or rectangular wire so produced can be packed or wound closer thanround wire so that in winding coils such as instrument coils and the like, more rectangular wire than round wire can be applied for equal coil volume or size.

A suitably coated 2 mil wire may be continuously drawn to one-quarter its original crosssection without impairing the insulation while a wire 18 mils in diameter coated with 1.0 mil layer of the enamel may be reduced by drawing to a diameter of 11.3 mils without breaking the enamel film. The extremely fine wire is particularly useful, in that instrument coils now may be wound from previously and uniformly insulated wire of a size heretofore unattainable. Some increase in the length of the insulated condeuctor is noted with any of the above treatments. This increase may amount to approximately 20 per cent in certain instances.

In the accompanying drawing, Figure 1 illustrates one arrangement whereby a coated wire of circular cross-section may be converted into an insulated wire having a substantially rectangular cross-section, while Figure 4 shows an arrangement whereby a similarly coated wire may be reduced in cross-sectional area. The remaining Figures 2, 3, 5 and 6 are enlarged views of the insulated wire before and after being subjected to mechanical working. For example, a conductor I provided with the preferred baked organic enamel 2, originally having a circular crosssection as shown in Figure 2 will, after a suitable number of passes between rolls 3 and 4 as wise, an insulated wire such as shown in Figure 5 may have its cross-sectional area reduced as shown in Figure 6, by passing the wire through a wire drawing die such as the die shown in crosssection in Figure 4, in which aproperly drilled diamond 5 is mounted. in a support 6. It is to be understood that the shape or size of the insulated wire may be altered to even greater extent than indicated in the drawing.

The rolled conductor shown in Figure 3 or the drawn conductor of Figure 6 can be further worked to either a flatter or finer insulated conductor depending to some extent on the original size of the conductor and thickness of the baked insulating coating. When a considerable altering of the cross-sectional profile of the conductor is desired, it is usually best to obtain the desired result by a number of passes through progressively smaller dies or rolls. Further a rolled conductor, such as shown in Figure 3, may be made to assume a more rectangular shape by' passing it through a pair of rolls similar to those shown in Figure 1 positioned at right angles to the rolls previously used. In every instance it is to be noted that some reduction in the thickness of the enamel coating takes place. The important feature is that, by these methods, it is possible to prepare extremely fine or substantially rectangular wire having practically uniform and wholly continuous insulation thereon, which wire is superior to that prepared by the usual methods previously attempted wherein a liquid coating material is applied to a very fine or non-circular conductor in its final shape.

Asthe cold working of the copper wire may harden it to a springy condition, which is a disadvantage in winding coils or for many other uses, it is desirable to anneal the coated wire to soften it afterit has been cold worked. The anneal may be carried out by heating the springy wire in a high frequency electricv field ment will not impair or otherwise alter the desirable properties of the enamel nor will the film be broken by subsequent winding operations. The time required for the anneal will depend on the wire used but will ordinarily be less than one minute.

What I claim as new and desire to secure by Letters Patent of the United States is:

The method of forming an insulated conductor having a closely-adhering, uniform coating thereon which comprises coating a conductor with a liquid coating composition comprising the reaction product of an aldehyde and a hydrolyzed polyvinyl ester, baking said coated con-.

ductor to harden the coating thereon, continuously drawing said coated conductor through a wire drawing die to alter the diameter thereof, and annealing said drawn conductor.

WINTON I. PATNODE. 

